Perdana, F.W., Ayuni, S.D., Wisaksono, A. and Syahrorini, S. 2021. Prototype Social Distancing Reminder Using HC-SR04 Sensor At The Payment Counter Via A Smartphone. Procedia of Engineering and Life Science. 1, 2 (Jul. 2021). DOI:https://doi.org/10.21070/pels.v1i2.952.